1. Field of the Invention
The present invention relates to a motor driving circuit, and more particularly, to a motor driving circuit which controls to maintain driving operation of a motor for opening and closing a window of an automobile for a predetermined time.
2. Description of the Related Art
Conventionally, a window opening and closing mechanism for an automobile includes a window opening and closing motor, a motor driving control circuit which controls a driving operation of the motor, a window opening switch, a window closing switch, and an auto switch.
In the window opening and closing mechanism, the operation of the window opening switch enables one-polar driving current to be supplied to the window opening and closing motor via the motor driving control circuit, the window opening and closing motor rotates in one direction, and the window moves in an opening direction during operating the window opening switch. Further, the operation of the window closing switch enables another-polar driving current to be supplied to the window opening and closing motor via the motor driving control circuit, the window opening and closing motor rotates in another direction, and the window moves in a closing direction during operating the window closing switch.
If the window opening switch is operated, simultaneously therewith, the auto switch is operated, and then the operations of the window opening switch and the auto switch stop, the one-polar driving current is supplied to the window opening and closing motor via the motor driving control circuit, the window opening and closing motor thus rotates, and the window continuously moves in the opening direction. When the window reaches the entire opening position, it stops supplying the one-polar driving current to the window opening and closing motor, the window opening and closing motor stops rotating in the one direction, and the window stops moving. Similarly, if the window closing switch is operated, simultaneously therewith, the auto switch is operated, and then the operations of the window closing switch and the auto switch stop, the other-polar driving current is supplied to the window opening and closing motor via the motor driving control circuit, the window opening and closing motor thus rotates in the other direction, and the window continuously moves in the closing direction. When the window reaches the entire closing position, it stops supplying the other-polar driving current to the window opening and closing motor, the window opening and closing motor stops rotating in the other direction, and the window stops moving.
In the above-mentioned window opening and closing mechanism, the motor driving control circuit needs to switch the driving operation of the motor the window and the stop operation thereof at a proper timing so as to prevent an excessive load to the motor. There have been proposed some well-known motor driving circuits for the above driving operation of the motor.
In the motor driving circuit for detecting the current, a resistor for detecting the current with a low resistance is serially connected to the motor, a motor current which flows to the resistor for detecting the current from both ends thereof is detected as a voltage value, and the detected voltage value is supplied to a detecting circuit. Further, the detecting circuit determines a driving status of the motor based on the supplied voltage value. As a result, when it is determined that the motor stops, an instruction for stopping driving the motor is issued to the motor driving control circuit so as to stop driving the motor by the motor driving control circuit.
Further, a timer-type motor driving circuit uses a charging circuit having a capacitance element which is charged by a CR time constant, in place of detecting the current flowing to the motor. After a predetermined time for charging the capacitance element in the charging circuit, the instruction for stopping driving the motor to the motor driving control circuit is issued so as to stop driving the motor by the motor driving control circuit. At this time point, a voltage comparator compares a reference voltage with a charging voltage charged to the capacitance element in the charging circuit and the passage of the predetermined time is determined by switching the pole of an output as the comparison result of the voltage comparator.
In the well-known motor driving circuit for detecting the current, when a surrounding environment changes due to the variation of surrounding temperature, an operating characteristic of the motor changes and thus the motor current is not detected. The motor current is not always detected with accuracy, thereby entering an erroneously operating status.
In the well-known timer-type motor driving circuit, similarly, when the surrounding environment changes due to the variation of surrounding temperature, the charging circuit having the CR time constant enters the erroneously operating status. In this case, the motor does not stop driving at the time for stopping driving the motor and the motor stops driving before the time for stopping driving the motor.
Further, when an input changing voltage increases to a voltage higher than an input reference voltage from a voltage lower than it and an increasing speed of the changing voltage is relatively slow due to a peculiar characteristic of the voltage comparator, the output as the comparison result does not sharply change to the negative pole or zero pole from the positive pole at a certain time point due to the peculiar characteristic of the voltage comparator, but the output enters a changing status from the positive pole to the negative pole or zero pole, namely, a bouncing status through a status in which the comparison output becomes the positive pole and the negative pole or zero pole again and again for a short time period.
When the window opening and closing motor is switched to a driving status or a non-driving status based on the output as the comparison result in the bouncing status, the window opening and dosing motor is switched to the driving status or the non-driving status in accordance with the bouncing status of the output as the comparison result. Consequently, to the user the motor seems like it operates erroneously. In particular, when the window opening and closing motor is switched to the non-driving status (the motor stops driving) based on the output as the comparison result in the bouncing status, anarc is generated between contacts under the influence of the bouncing status and the contacts have a high temperature or a contact material is fused, by use of a contact-type switching element as an operation switching element. Thus, the life of the contact-type switching element is short.
In order to improve the above-mentioned adverse influence, means for connecting a feedback resistor between a non-inverse input terminal and an output terminal of the voltage comparator is well known. However, the means cannot completely improve the bouncing status which is caused in the output as the comparison result of the voltage comparator. Accordingly, the above means and another means must be used together, a large number of circuit parts are necessary in accordance with the simultaneous use of both the means, the circuit structure is complicated, and manufacturing costs are increased.
The present invention is devised in consideration of the foregoing technical background. It is an object of the present invention to provide a motor driving circuit which can always drive the motor and stop driving the motor with accuracy when the surrounding environment changes.
In order to accomplish the above-mentioned object, according to the present invention, a motor driving circuit includes: an opening switch which drives opening operation of an opening and closing member; a closing switch which drives closing operation of the opening and closing member; an auto switch which automatically drives the opening and closing member to a predetermined position; a motor which drives the opening and closing member by operating the opening switch, the closing switch, or the auto switch; a charging circuit which charges a first capacitance element by a first CR time constant when the opening switch is operated; and a discharging circuit which charges a second capacitance element when the auto switch is operated and which discharges a discharging voltage charged to the second capacitance element by a second CR time constant when the operation of the auto switch stops, wherein driving operation of the motor stops when a charging voltage of the first capacitance element is charged to a voltage higher than a first reference voltage or when the discharging voltage of the second capacitance is discharged to a voltage lower than a second reference voltage, upon the driving operation of the motor.
With the above-described structure, the motor driving circuit includes the charging circuit for charging the first capacitance element by the first CR time constant and the discharging circuit for discharging the discharging voltage charged to the second capacitance element by the second CR time constant. The driving operation of the motor and the stop operation thereof are set by use of both the charging voltage of the first capacitance element in the charging circuit and the discharging voltage of the second capacitance in the discharging circuit. Therefore, when the surrounding environment changes due to the fluctuation of the surrounding temperature and the change in surrounding environment influences on the charging characteristic of the first capacitance element in the charging circuit and on the discharging characteristic of the second capacitance element in the discharging circuit, the effects on the charging circuit from the above change and on the discharging circuit are reverse to each other and they are mutually eliminated. Thus, it is capable of obtaining the motor driving circuit which drives the motor and stops the driving operation thereof with accuracy, entirely without the influence of the surrounding environment.
Further, with the above structure, in the motor driving circuit, time for requiring that the charging voltage of the first capacitance element reaches the first reference voltage after operating the opening switch is set to be longer than time for requiring that the opening and closing member reaches the predetermined position.
Alternatively, in the motor driving circuit, time for requiring that the discharging voltage of the second capacitance element reaches the second reference voltage after stopping the auto switch is set to be longer than time for requiring that the opening and closing member reaches the predetermined position.
With the structure, the opening and closing member can accurately move to the predetermined position.
Further, the motor driving circuit includes the operation switching element which switches the operation of the motor, and the charging voltage of the first capacitance element and the discharging voltage of the second capacitance element are discharged via the operation switching element. Consequently, the influence of the bouncing status is eliminated.
Furthermore, according to the present invention, the operation switching element is a relay having a driving coil and a bipolar switching type contact in addition to the foregoing structure, so that the charging voltage of the first capacitance element and the discharging voltage of the second capacitance element are discharged via the driving coil. Since the charging voltage of the first capacitance element and the discharging voltage of the second capacitance element are discharged via the driving coil in the relay, the structure is extremely simple.
In order to accomplish the object, a motor driving circuit includes: an opening switch which drives opening operation of an opening and closing member; a closing switch which drives closing operation of the opening and closing member; an auto switch which automatically drives the opening and closing member to a predetermined position; a motor which drives the opening and closing member by operating the opening switch, the closing switch, or the auto switch; an operation switching element which is connected to the motor and switches operation of the motor; a charging circuit which charges the first capacitance element when the opening switch is operated; and a voltage comparator which compares a charging voltage of the charging circuit with a reference voltage, wherein an output from the voltage comparator stops driving operation of the motor and the charging voltage of the charging circuit is discharged via the operation switching element when the charging voltage of the charging circuit reaches a voltage higher than the first reference voltage upon the driving operation of the motor.
With the above-described structure, the motor driving circuit includes the charging circuit which charges the capacitance element upon operating the switch for opening the opening and closing member and the voltage comparator which compares the charging voltage of the charging circuit with the reference voltage. When the charging voltage of the charging circuit increases to the reference voltage upon driving the motor, the output as the comparison result generated from the voltage comparator stops the driving operation of the motor and the charging voltage of the charging circuit is discharged via the operation switching element. Thus, the output as the comparison result of the voltage comparator is in the bouncing status. When the operation switching element stops the driving operation of the motor in accordance with the bouncing status of the output as the comparison result, at this time point, the charging voltage of the charging circuit is discharged via the operation switching element. Consequently, the bouncing status of the output as the comparison result is masked by this discharging operation and the operation switching element promptly stops the driving operation at a certain time point without the influence of the bouncing status. A user does not sense that the window opening and closing motor is erroneously operated.
The charging voltage of the charging circuit is discharged via the operation switching element so as to eliminate the influence of the bouncing status. Hence, a large number of circuit parts are not required and the circuit configuration is not complicated.
Further, in addition to the above structure, the operation switching element is a relay having a driving coil and a bipolar switching type contact, and the charging voltage of the charging circuit is discharged via the driving coil in the relay according to the invention.
With the above structure, since the charging voltage of the charging circuit is discharged via the driving coil in the relay, the circuit configuration is extremely simple.
Further, in addition to the above structure, when the motor is driven, the time for requiring that the charging voltage of the charging circuit reaches the reference voltage is set to be longer than the time for requiring that the opening and closing member reaches the predetermined position.
With the above-described structure, the opening and closing member moves to the predetermined position without fail.